MC9S12XD256MAL Datasheet, PDF (1292/1348 Pages) Freescale Semiconductor, Inc – Freescale’s Scalable Controller Area Network

Appendix C Recommended PCB Layout
Appendix C
Recommended PCB Layout
The PCB must be carefully laid out to ensure proper operation of the voltage regulator as well as of the
MCU itself. The following rules must be observed:
• Every supply pair must be decoupled by a ceramic capacitor connected as near as possible to the
corresponding pins (C1–C6).
• Central point of the ground star should be the V_SSR pin.
• Use low ohmic low inductance connections between V_SS1, V_SS2, and V_SSR.
• V_SSPLL must be directly connected to V_SSR.
• Keep traces of V_SSPLL, EXTAL, and XTAL as short as possible and occupied board area for C7,
C8, and Q1 as small as possible.
• Do not place other signals or supplies underneath area occupied by C7, C8, and Q1 and the
connection area to the MCU.
• Central power input should be fed in at the V_DDA/V_SSA pins.
1294
MC9S12XDP512 Data Sheet, Rev. 2.21
Freescale Semiconductor